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French nuclear firm trying to fix 'performance issue' at China plant
A French nuclear company has said it is working to resolve a "performance issue" at a plant it part-owns in China's southern Guangdong province after an earlier report of a potential leak there.
Framatome, a subsidiary of the energy giant EDF, told Agence France-Presse news agency that it was "supporting resolution of a performance issue" at the plant. "According to the data available, the plant is operating within the safety parameters," it said, adding that an extraordinary meeting of the power plant's board had been called "to present all the data and the necessary decisions".
The statement came shortly after the US TV network CNN reported that Framatome had previously warned the US energy department of an "imminent radiological threat" in a letter.
According to CNN, the letter included an accusation that the Chinese safety authority was "raising the acceptable limits for radiation detection outside the Taishan nuclear power plant in Guangdong province in order to avoid having to shut it down".
(Score: 2) by Rich on Wednesday June 16 2021, @03:12AM (2 children)
To my understanding (I might be wrong), the zirconium tubes in which the fuel pellets are kept are hermetically sealed. Xenon-135 would not be vented at all, but go through the decay process and end up as solid. Certain reactors of eastern european origin had obscure entries in their manual that the reactor should not be re-started after a shutdown until after a waiting period (i.e. the xenon decay is over), and when some guy orders to ignore that, for example to repeat a safety test, shit can happen. There is no deliberate Xenon venting to accelerate the wait.
The industry eventually figured out that fuel elements DO break, not very often, but often enough, so they use scavengers to get the nasty stuff out of the primary coolant. As I read and understand the almost nonexistent press information, they have seen a lot more xenon than they have expected. Apparently they also reduced the power output. Putting one and one together, I assume they figured out that the fuel elements break at full load and came up with an engineering calculation how far they can push it. I would assume there is a predetermined breaking point for overpressure, so they might have hit that. If it is something else, it is bad. Control/safety rods might get stuck, which wouldn't mean an immediate meltdown, but they'd have to inject boric acid for a safety stop, and then the plant would be down for a major overhaul.
Also, this is all French technology. But I've been wondering why the EPRs at Olkiluoto, Flamanville, and Hinkley Point are major screwups, while Taishan went up on schedule. If the Chinese can ask Areva/EdF to straighten that out, that might cost the French more than they have. Then they'll demand nuclear subsidies from the EU, which might make people on course for the next German government VERY unhappy....
(Score: 1) by khallow on Wednesday June 16 2021, @12:41PM (1 child)
Not quite buying that. In a normally operating reactor, Xe-135 would absorb a neutron and become Xe-136 which is also a gas. If enough of that builds up, then your hermetically sealed fuel rods will rupture. But those rods get replaced regularly so I don't see it as a problem.
Looks like we have the answer to that. Because the Chinese are a bit more cavalier about such things like safety (and have a far weaker anti-nuke lobby).
Demanding something doesn't mean you'll get it. And China isn't operating in a way to minimize the cost of the resulting mess - that reduces any liability for France. They'll have a weak case for making demands, particularly, if the expertise and resources for cleaning up the mess has to come from outside China.
I don't quite understand the dynamics, but it sounds like you can get into some serious trouble when you do a quick restart after shutting down a reactor. In the few hours after the reactor is shutdown, Xe-135 would build up due to decay of other isotopes (which have a short half life as well). So you would temporarily have elevated levels of Xe-135 in the fuel rods.
Because Xe-135 is a strong fission poison, you have to run the reactor at significantly higher power (well, denser configuration of fuel rods) than normal in order to get the same level of fissioning - because the Xe-135 is absorbing a lot of the neutrons you would need to maintain criticality. Then once enough of the Xe-135 burns off (gets converted to Xe-136 by neutron absorption), the reactor will suddenly revert to normal criticality behavior with a substantial surge in power.
Maybe modern military nuclear reactors are designed to accommodate high Xe-135 operation (because you could be very dead, if you have to wait six or more hours to restart your nuclear reactor), but I doubt there are any civilian reactors designed for this sort of power surge, because you can save a lot of money and engineering by never operating the reactor in that way.
(Score: 2) by Rich on Wednesday June 16 2021, @01:21PM
I followed up, the tubes definitely should be fully sealed:
https://www.tandfonline.com/doi/pdf/10.1080/18811248.2010.9711953 [tandfonline.com]
Money quote:
This is for a CANDU, but I assume PWRs are not much different. PWRs also run at much higher pressures (300 bar), so a tiny bit of temporary gas buildup is completely irrelevant to the zircaloy tubes, even more so than in CANDUs. It seems the endcap sealing is a science in itself, so it's a good bet they assume these problems have to do something with those.
Haha. You have no idea how much German taxpayer money went down the drain to make issues go away, even when someone just was loudly whining. And when the French want the Germans to pay for their atomic mess, some green-aligned German heads will explode. They'll probably do a backroom deal and allow the ECB to "print" a few billion € for the French. (I'm simplifying, it's not called "print"ing anymore, I think the latest term was "quantitative easing").
This is designed in. The relevant discoveries about Xe-135 behaviour were made at Hanford (iirc, the Rhodes book is really good, they wondered why the reactor suddenly stopped) and Chernobyl (they wondered why the reactor suddenly blew up).